1. Field of the Invention
The present invention relates to a novel glycophospholipid wherein glycerophospholipid links to a sugar molecule, and a process for preparation thereof. The glycophospholipid according to the present invention is useful as a biochemical reagent, a raw material for medicine and foodstuff, or a surfactant.
2. Background of the Invention
Phospholipids have various functions in organism. Phospholipids such as phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, as a component of biomembrane, form bimolecular lipid membrane to protect cell membranes from external environment, thereby providing suitable environment for functioning of the protein. In addition, they are known to function as a resource of choline, phosphorus, fatty acids, and function as a depot of arachidonic acid for biosynthesis of prostaglandins. Recently, control mechanism of cell differentiation has been gradually revealed. Moreover, some phospholipids such as PAF (platelet activation factor) themselves demonstrate strong physiological activity. Accordingly, phospholipids have various important functions in organism.
Glycolipids are also ingredients of cell membrane. These glycolipids on the external surface of the cell membrane are considered to function as surface markers of cells because of the variety of sugar chain and of the different patterns of sugar chains expression according to the kind of cells. The differentiated cells express a specific glycolipid on a surface of the cell. The fact suggests that glycolipids have various cell functions. For example, function as a receptor, to control activity of membrane bound enzyme, to control ion channel, to control membrane fluidity, to control cell differentiation, etc.
Glycolipids are general name for materials containing both water-soluble sugar chain and fat-soluble group in a molecule. In animal cells, most of glycolipids are sphingolipids, containing sphingosine. Glyceroglycolipids, containing glycerol, are only found in vegetables, bacteria, etc. Recently, glyceroglycolipids have been considered to have some physiological activities in animal cells, for example, since seminolipid is found to exist in porcine testes. In connection with phospholipid and sugar, it is found that phosphatidylinositol functions as an anchor (GPI anchor) which links to protein through inositol binding sugar chain in a molecule to connect protein to cell membrane. Structural analysis of various GPI anchors such as those of Trypanosoma membrane antigen, human red cell acetylcholine esterase, etc. have been reported. The protein can move on a surface of a membrane, so GPI is considered to control the enzymatic activity and function as a receptor. Up to date, however, compounds wherein sugar links to glycerophospholipid have not been found. There are no report on existence of glycolipid in milk of mammal, for example in cow's milk.
The present inventors have found a material exhibiting color reaction characteristic to phospholipid and sugar by thin layer in isolated and purified fractions chromatography from milk, and have isolated a fraction of phospholipid by repeating purification and isolation according to compound lipid purification methods mainly including column chromatography. As a result of structural analysis of these fractions, It was confirmed for the first time that unknown glycophospholipid exist in milk.
Accordingly, the present invention relates to a novel glycophospholipid, particularly glycophospholipid wherein sugar links to glycerophospholipid, and intends to provide a process for preparing such glycophospholipid.